roots in the chechnya region of russia. olderbrothertamerlanvisiteddagestan in 2012 a region in southern russia where his father and mother still live. in an interview with "the wall street journal" their mother said tamerlan had given your boxing and drinking and smoking as he turned to a religious life and told the paper he phoned her the night he died saying, quote, the police, they have started shooting at us. they are chasing us. telling her he loved her before the phone went silent. and his uncle who lives in maryland says he believes the older brother became radicalized in cambridge and not overseas and eventually drew in his younger brother but lawmakers say more questions about their past need to be answered. >> we believe they may have traveled on an alias to get back to his home country and that seven months, six and a half months or so becomes extremely important. so you know he had some radicalization before he left, you know he probably didn't travel on his own name or some variation of his own name, and when he comes back, he has a renewed interest in that radi

off, a surveillance camera shows dzhokharandtamerlantsarnaevwalking toward the boston marathon finish line with backpacks. then a surveillance camera mounted on the restaurant nearby captures crucial pieces of evidence. seven minutes before the first bombing the video which still hasn't been released shows dzhokhar walking toward the second bombing site. three minutes later he works his way into the crowd and takes his backpack off. the fbi says still photos show the backpack on the ground at his feet. when the first bomb goes off, tsarnaev remains calm as the people around him respond to the blast. he walks away without his backpack and ten second later the second bomb goes off in the spot where he left the backpack. complaint reveals that agents searched dzhokhar tsarnaev's u. mass dartmouth dorm room and they found bbs and large pyro tech. investigators found a bomb of the same brand of pressure cooker used in the bombs in the thursday night shoot-out. >> within minutes i had six of my officers, four on duty, two off duty, that are engaged in this gun fight. it continues and

with colleagues andfriends.tamerlanwentback to his house. and you would not have known they had just conducted one of the most significant terrorist attacks on u.s. soil. so the psychological profile here is something that's also going to get a tremendous amount of attention. >> we have from pete williams the breaking news that he is, the suspect they currently have is cooperating, saying they acted alone, they did not have any foreign assistance, they didn't seek any foreign guidance, got instructions for bomb making on the internet. do the facts as you know them now synch with that? >> yeah, from what we know i think that is all part and parcel of the story, and i think also we would have heard pre-miranda whether or not during the public safety exception if he had provided any information about imminent threat, additional plans, additional co-conspirators. because we haven't heard from any government sources on it, we should conclude there was nothing else in terms of imminent threat. the next step is to get all of the statements from tsarnaev and then corroborate them. to corroborate them

to the one in the surveillance photos he was allegedly wearing. investigators also want toquestiontamerlantsarnaev'swife. the couple initially met at a nightclub. she later converted to islam, dropped out of college and had a child with him. her attorney has said that she had no suspicions that her husband might be plotting an attack. hundreds of people stood in silence at copley square at 2:50 p.m. one week after the bombings. president obama marked the moment of silence from the white house. the u.s. senate held a similar tribute on capitol hill. >>> it is still unclear what impact the boston bombings will have on the immigration debate in congress but the topic of national security is clearly playing a more rom neprominent n the discussion. things got tense on capitol hill yesterday when senator chuck schumer sparred with republican senator chuck grassley about the future of the legislation. take a look. >> a few ways to improve the bill, offer an amendment when we start mark-up in may and let's vote on it. i say that particularly to those who are pointing to what happened, the terrib